GB2216710A - Read/write system for flexible optical/magneto-optical media - Google Patents

Description

OPTICAL OR MAGNETO-OPTICAL DATA SYSTEM The present invention relates to the field of optical information storage systems.

The present emphasis in the development of information storage systems is the capability to store more and more information into a so-called "desk top" sized computer memory system. Those "desk top" sized memory systems which incorporate magnetically recorded hard disc media, such as that used in Winchester disc drive type memory systems1 currently have the capacity to store upwards of 20 megabytes of magnetically recorded information. The probl 5 with such memory systems is that by necessity th award disc media is permanently mounted into the computer. Since the media is not easily removable, the user is limited to whatever portion of tbe hard disc is remaining for information storage at the time of use.Accordingly, magnetically recorded hard disc media information storage systems are not viewed as a potential solution to increasing information storage capacity.

So-called "floppy" disc memory systems wherein flexible discs, each having a diameter of either 5.25 inches or 3.50 inches, are used as the storage media provides easily removable storage media. However, the problem with such storage systems is that the present storage capacity of information magnetically recorded on a single floppy disc used in such a system has not yet reached a level equal to that of the hard disc, ie a single floppy disc media can only store approximately 1 to 2 megabytes of magnetically recorded information.

Systems for storing information which can be accessed through optical devices have received significant attention due to their potential capacity to store substantially more data, ie on the order of 400 to 800 megabytes of information, than that Available in either magnetically recorded hard disc or floppy disc storage systems. One reason for the significantly increased storage capacity of optical storage systems is that the diameter of a beam of focussed light to be used to read or write information is typically only 1 micrometer (micron). Consequently the density of information stored on a media is much greater than a typical magnetic recording density. Additionally, the media for use in such optical systems can be of a form similar to that of a so-called floppy disc, that is a media which is easily removable.Unfortunately, major problems continue to plague the development and commercial acceptance of such optical systems, namely the relative slowness by which information can be retrieved compared to magnetic storage systems, the current size restrictions of so-called "desk top" computers and the ability to write/erase and rewrite information many times on a single piece of media.

Consider first the current size restrictions.

So-called "desk top" computers have been provided with a number of modular components, particularly including information storage systems, which can be added into the casing of the computer to provide a certain degree of customizing to fit a particular need. Since such components can have any one of a number of sizes, the American National Standards Institute has adopted certain external standard dimensions with regard to such components, which standards are generally referred to as full-height and half-height standards. Since the half-height standard appears to be the most desirable for such modular components, a need exists to develop an optical information storage system which will fit into the half-height standard. The half-height standard for modular components is as follows: height 1.625 inches; width 5.75 inches; and depth 8.00 inches.The problem with current optical storage systems is that present designs and techniques require components which when assembled easily exceed this size standard. It appears that only a few of the currently available systems include an optical head assembly, which is only one component of an optical storage system, which would fit into such a size standard.

Consider now the relative slowness by which information can be retrieved in current optical information systems compared to magnetic storage systems. The primary factor contributing to the slow access problem of present optical storage systems is the weight of the optical head assembly. As will be appreciated, the greater the weight of a device for reading from or writing to an optical disc, the more difficult and consequently slower it will be to orient such a device in relation to precise locations on a rotating disc.

Present optical storage systems include those found in video disc or compact disc (CD) players, which are of the read only variety and those which are termed write once read many times (WORM) optical storage systems. Presently the ability to write and read many times to and from an optical disc is primarily limited by the media available for use in such systems although it is to be understood that the present invention is not limited only to media which currently exists.

In present CD systems an optical disc is rotated about a central axis. A laser beam is projected onto the surface of the disc by means of a lens, a reflecting mirror or beamsplitter, and a projection lens. The laser beam is modulated by the information stored on the optical disc and the modulated light is detected by a photodetector. Output signals from the photodetector are provided to a processor for producing information signals and tracking signals. The source of the laser beam, the lens, the mirror, the projection lens and the detector are collectively referred to as an optical head assembly. The optical head assembly is typically moved radially across the rotating disc in order to access the information stored on the disc.

Since the information to be read or written on an optical disc is contained in narrow tracks, coarse and fine radial movement mechanisms are provided. Hitherto, it has not been possible, or even considered desirable, to combine coarse and fine movements into one mechanism.

The coarse radial movement mechanism typically includes either a pivoting arm or a radially oriented track which moves the optical head assembly radially across many tracks. The fine radial movement mechanism generally operates to move the projection lens either along a radial axis, which causes the projection lens to move between a few adjoining tracks, or along an axis generally perpendicular to the disc, which allows the projection lens to dynamically focus the laser beam on the surface of the disc during operation. Such fine movement mechanisms can be found in the commercially available optical head assemblies sold by the Olympus Corporation of Lake Success, N.Y. (TAOHS Series) or Pentax Teknologies of Broomfield, Col. (W-108-02 Series). An example of such an optical head assembly can also be found in U.S. Patent No 4,092,529 - Aihara et al. The height of these fine movement mechanisms also contributes to the size restriction problem. Reference is also made to the WORM optical storage system shown in Rosch, Winn L., "WORN's for Mass Storage" PC Magazine, Vol 6, No 12 (June 23, 1987) pages 135-148.

Since the fine movement mechanism typically causes movement of the projection lens through the use of relatively massive electro-magnets, the overall weight of the optical head assembly is such that movement of the assembly is cumbersome and thus relatively slow. In an attempt to resolve the access time problem, efforts to reduce the optical head assembly have been reported. However, since the fine movement mechanism is still an essential component, the weight and size contributed by such a mechanism remains.

For example, Fukui, Y et al, "New servo method with eccentricity correction circuit" Optical Engineering, Vol 26, No 11 (November 1987) pages 1140-1145 discloses an optical head assembly which describes the combination of an anamorphic prism, a convex lens and a roof shaped prism in an effort to determine data and tracking information signals from a single light beam. Such a combination appears to result in fewer optical components; however, the size and weight of the fine movement mechanism remains.

Writing information onto a disc with current optical systems typically is achieved by burning the information into the media. Presently available media has not been developed where such burning can be easily erased and rewritten.

A hybrid of the optical and magnetic information storage systems. so called magneto-optic information storage systems appear to have the potential to not only resolve the desire for increased storage capacity but also the need to erase optical information and rewrite new optical information. It has been estimated the theoretical upper limit of the storage capacity of such systems can be as high as 300 megabytes per square inch of media. However in practice on a 5.25 inch floppy disc yields of approximately 400 to 800 megabytes can be expected.

In magneto-optic storage, data are recorded and erased on a thin film of magnetic material having properties to be described herein. Similar to magnetic recording, information is stored as a sequence of bits, where the magnetic field of the film at a given point is either north-pole-up (a digital 1) or north-pole-down (a digital zero). A blank disc has all of its magnetic poles pointing north pole-down. The drawback with magneto-optic media is that the magnetic field required to flip one magnetic domain from north-pole-down to north-pole-up, ie the coercive field, varies greatly with temperature. At room temperature, the coercive field necessary to achieve a north pole flip is so high that an ordinary magnet is too weak.At approximately 1500C, the coercive force required to flip a domain falls almost to zero and a bit can be recorded using known magnetic recording techniques.

Optical techniques are used in a magneto-optic system to heat selected spots on the media which is passing close to a relatively large electro-magnet. In this way, a point on the media can be heated, lowering the coercive field required to write a bit of information and the magnet, depending on its own north pole orientation, can so record the desired bit. Once the laser beam is turned off, the just heated point on the media cools "freezing" the oriented north pole to the desired orientation. To erase information so recorded, the process need only be reversed, that is the point on the media will be heated by the laser beam and the magnet's north pole orientation will be such to orient media based north poles in a down orientation.

Since it is undesirable to have any contact with the media, relatively large electromagnets were utilized. Since such magnets are relatively slow in changing their own pole orientation according to the electrical signal being provided, poles on the media are oriented by modulating, eg turning on and off, the laser while the magnetic field remains relatively constant.

Reading information so recorded on a magneto-optic disc is achieved solely through optical components. A lower power light beam is focussed onto the media. The reflected light is read from either above or below the media. Because of phenomena known as the Kerr magneto-optic effect and the Faraday effect light reflected from the media or passing through the media will have a slightly different polarization than the light being focussed onto the media. The change in polari tion will be either clockwise or counterclockwise depending on the north pole orientation at that point. For a more graphical interpretation of the above described magneto-optic operation, reference is made to Freese, Robert P, "Optical disks become erasable", IEEE Spectrum, February, 1988, pages 41-45.

The problem with such magneto-optic information storage systems is the ability to overwrite information without having to make two passes over the same point on the media. Hitherto, the primary method for overwriting information in a magneto-optic system was a two step process. First, a pass was made over the media to erase all information in a given track. Second, another pass was made over the same points to now record the desired information. Since during magneto-optic recording the laser is turned on and off at a high frequency while the media is continuously moving over an electromagnet having a relatively constant magnetic field, the two step process was the primary method of assuring that no unwanted information remained on the disc after the overwrite operation was completed.

Attempts to resolve this problem included the use of two optical heads and associated electromagnets apparently arranged in a lead/lag fashion, so that the lead head can erase in the same media pass wherein information is written. Another attempt to resolve the two pass problem was the proposed use of side by side light beams focussed on adjacent tracks. Still another proposal for resolving this problem was to keep laser power constant while modulating the magnetic field. This latter proposal has been rejected in Kobori, Hiromichi et al. *New magneto-optic head with a built-in generator for a bias magnetic field", Applied Optics, Vol 27, No 4 (February 15, 1988) pages 698-702. The reason given for the rejection was that to obtain high data bit rates, the magnetic fiend generator (magnetic head) had to be located in close proximity to the media.Consequently it would be difficult not only to adopt a double sided disc but also to preserve disc removability.

Consequently a need still exists for a magneto-optic storage system which is capable of overwriting previously stored information with only one pass without the problems of size and access times found in other optical storage systems.

According to a first aspect of the present invention there is provided an optical read/write storage system for reading and writing data to and from a flexible optical or magneto-optical media, comprising: an optical read/write head for providing focussed light onto said flexible media and for receiving reflected light from said flexible media; and fine stabilisation means, associated with or connected to said optical head and positioned proximate said flexible media, for stabilizing said flexible media in a desired position so that said optical head need not be moved substantially toward or away from said media in order to maintain said light focussed on said media.

According to a second aspect of the present invention there is provided an optical read/write storage system for reading and writing data to and from a flexible or magneto-optical media, comprising: an optical read/write head for transmitting focussed light onto said flexible media and for detecting light gathered from said flexible media; and fine stabilization means1 associated with or connected to said optical head and positioned proximate said flexible media, for stabilizing said flexible media in a desired position so that said optical head need not be moved susbtantially toward or away from said media in order to maintain said light focussed on said media.

According to anot: .r aspect of the invention there is provided an information read/write storage system for reading and writing data to and from a flexible magneto-optic media, comprising: a magnetic recording means, having a recording head positioned proximate said media, for recording information onto said media at a point, said point being defined as the area of said media wherein information is being recorded at any given time; and an optical read/write means for providing focussed light onto said media during reading and writing, for receiving reflected light from said media to read said information and for continuously providing focussed light onto said media for heating said point while said magnetic recording means is recording.

Embodiments of an optical information storage system according to the invention may be capable of either reading from or writing onto optical media at speed3 comparable to magnetic storage systems, may have a low weight optical head assembly and may readily be manufactured to dimensions meeting the half-height standard.

It will be seen from embodiments described herein that an optical or magneto-optical information storage system can be provided which eliminates the need for a dynamic focussing mechanism by precisely stabilizing a flexible optical media during read/write operations, said stabilization being provided on a primary and secondary level, both of which involve the suspension of said media on an air bearing created by means of the Bernoulli principle.

The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a perspective view of an optical information storage system in acco-dance with the pres L invention; Figure 2 is a diagrammatic view of the storage system; Figure 3 is a perspective view of a portion of the system shown in Figure 1; Figure 4 is a section view along the line 4-4 of Figure 3; Figure 5 is an enlarged view of a portion of the coupler shown in Figure 3; Figure 6 is a diagrammatic view of the optical components shown in Figure 3; Figure 7 is a side view of an alternative embodiment of the optical components shown in Figure 6; Figure 8 is a top view of another alternative embodiment of the optical components shown in Figure 6;; Figure 9 is side view of another alternative embodiment of the optical components shown in Figure 6; and Figure 10 is a perspective? view of a portion of the magneto-optical information system version of the system shown in Figure 1; Figure 11 is a section view along the line 11-11 of Figure 10; Figure 12 is an enlarged view of a portion of the coupler shown and magnetic head in Figure 10; and Figure 13 is a side view of an alternative embodiment of the magneto-optical system.

An information storage system constructed in accordance with the principles of the present invention is shown in Figure 1 and generally designated 10. A cartridge 12 is shown to be partially inserted in disc drive housing 14 such that slidable cover 16 has begun to move laterally. When such lateral movement is completed, an opening 18 (shown in Figures 2-4) will be exposed allowing flexible media disc 20 to be operated upon.

A central hub 22 is provided in disc 20 for engagement by drive spindle 24 when cartridge 12 is fully inserted into housing 14 for rotation of disc 20.

The bottom cover 26 of housing 14 is shown as being partially cut away in order to expose spicule member 28 which serves to guide cartridge 12 during insertion and arm 30 during access of disc 20. Although not shown in complete detail in Figure 1, a head assembly 32 is mounted at the distal end of arm 30. A linear actuator motor 34 serves to move arm 30 in spicúle member 28 so that head assembly 32 is moved radially across the surface of disc 20. While several types of linear actuator motors are available for use with the invention, it is preferred that the linear actuator motor chosen be capable of providing both coarse and fine movements of arm 30 for both track seeking and.

track following by head assembly 32. The range of movement of arm 30 is from the retracted position shown in Figure 1 to an extended position such that the distal end of arm 30 strikes stop 36.

The details of construction of cartridge 12, specifically its integrally formed Bernoulli surface, and its insertion and engagement by the various disc drive components described above is more fully detailed in the following: US Patent Nos 4769733; 4740851; 4743989; 4740851; 4658318; Disk Drive Motor Mount McCurtrey et al, filed April 21, 1986 US Patent Application Serial No 854342; Disk To Spindle Engaging Device - Jones et al, filed April 21, 1986 US Patent Application Serial No 854333; and GB Patent Application No 2190232, which Patents and applications are incorporated herein by reference. Also incorporated by reference is patent application Disk Cartridge - Bauck et al, filed December ' , 1986 having Serial No 947by2 which application is related to US Patent No 4658318 for Magnetic Disk Cartridge - Bauck issued April 1, 1986.

Since those applications are primarily concerned with magnetically recorded information storage systems, the media (the applications disclose the use of dual floppy discs in a single cartridge) and the means for reading and writing data from or to the media will be different.

Otherwise, the structure used in those devices will be substantially identical to that which can be incorporated in a storage system in accordance with the present invention. It is assumed that one can substitute a single floppy disc for the dual media shown in those applications.

A commercially available disc drive/cartridge for magnetically recording information which can be modified to provide an optical or magneto-optical information storage system in accordance with the present invention is the Beta-20 System manufactured and sold by IOMEGA Corporation of Roy, Utah, USA. It will be understood that the circuitry and programming, utilized in the Beta-20 System to convert the analog signals generated by magnetically recorded information, to a digital signal, will require modification so that the analog signals generated by optically recorded information can also be converted into a digital signal. The technology for converting such optically generated analog signals to digital signals is known.

Consider now the optical information storage system shown diagrammatically in Figure 2. Disc drive motor 40 causes disc 20 to rotate. Such rotation is initiated by an appropriate enabling signal from processor 42. As disc 20 is rotating, processor 42 provides an enabling signal to linear motor 34 causing optical head assembly 32 to move radially across the surface of disc 20. Head assembly 32 illuminates a limited area on disc 20 with a bam of light, in a manner to be described hereinafter, in response to a further enabling signal from processor 42. Information stored on disc 20 modulates the light reflected off the surface of disc 20, which reflected light is detected and converted into an electrical signal by head assembly 32 and provides such signal to processor 20.There are several known methods for achieving this operation and the present invention is not limited to use of any particular method. Similarly, the present invention is not limited to the use of any particular method for storing information on disc 20. Processor 42 causes disc 20 to spin, causes linear motor 34 to move head assembly 32 radially across disc 20 and causes head assembly 32 to write desired information onto the surface of disc 20.

Where the system is a magneto-optical system, in the preferred embodiment, the conversion into an electrical signal of the reflected light is accomplished by way of a differential detection scheme. It will be recalled that light reflected either from or transmitted through a magneto-optic disc at a point where information has been written will have a slightly different polarization than the light being focussed onto the media. The change in polarization will be either clockwise or counterclockwise depending on the north pole orientation at that point. By passing the reflected light through a beamsplitter, detecting each of the split beams and comparing the detected beams, it is possible to determine whether the reflected light has had its polarization modified indicating the presence of a digital 1 stored on the disc.Since this type of detection scheme has been described in reference to another magneto-optic device in Mansuripur, M et al.

"Signal and noise in magneto-optical readout", Journal of Applied Physics, Vol 53 No 6 (June 198.; pages 4485-4493 it will not be further detailed herein.

Figures 3-9 refer to an optical information system. As shown in Figure 3, cartridge 12 has been fully inserted and arm 30 has been extended such that the optical head assembly 32 has been moved radially across the surface of disc 20. Optical head assembly 32 is shown to include laser diode 44 having leads 46.

Although not shown it will be understood that leads 46 are electrically connected to processor 42 for operation in any one of several known ways. Laser diode 44 serves as a source of light for optical head assembly 32. As used herein the term light is meant to include both visible and invisible light or more precisely electromagnetic radiation. More particularly, the term light is meant to include that light having a wavelength in the range from 200 to 2000 manometers (nm).

As shown in Figures 3, 4 and 6, the light emitted from laser diode 44 is passed through an aperture plate 48 which serves to limit the diameter of or to collimate the beam to a desired dimension, which in the preferred embodiment is equal to the smallest allowable beam diameter in the optical system. Light passing through aperture plate 48 is further collimated by lens 50 and provided to polarizing beamsplitter 52 where it is reflected towards or in the direction of disc 20. The light which is reflected by polarizing beamsplitter 52 is then passed through quarter wave plate 54 which operates, as is known. so as to change the plane of polarization of the light.After reflection, light passing back through quarter wave plate 54 will have had its polarization plane retarded by 90 and thus will pass through the mirror surface contained in beamsplitter 52 and not be reflected back onto diode 44.

Light passing through quarter-wave plate 54 towards disc 20 will next pass through lens 56, whereupon the light is focussed onto the surface of disc 20. Unlike previous optical storage systems. lens 56 is not mounted in fashion so as to be moved relative to arm 30. In this regard lens 56 is stationary in relation to arm 30. Light reflected off or from the surface of disc 20 is then collimated by lens 56 and passed through quarter-wave plate 54. As previously described, since the plane of polarization of the light is now retarded by 900, it will pass through beamsplitter 52 and be focussed by lens 58 onto detector 60. The lenses 56 and 58 may be gradient index lenses.

While detector 60 can be of several different types, one detector used is the model IT338 manufactured and sold by Sony Corporation. Such a detector serves t detect, ie discern, both data as well as tracking information. Detector 60, in turn, generates electrical signals which are reflective or indicative of the detected data and tracking information. These signals are then transmitted via leads 62 to processor 42.

Consequently, the signals from detector 60 not only serve to provide the accessed information, but also allow processor 42 to evaluate the tracking information and provide or supply the appropriate signals to linear motor 34 for moving arm 30 in a manner so that optical head 32 can be radially positioned over and follow a desired track on disc 20. Lens 56 is shown in Figure 4 to be securely mounted in coupler 64 which. in turn, is securely mounted in arm 30.

While not shown it will be understood that an opaque cover member may be provided over optical head assembly 32 in order to block out stray light as well as to protect optical head assembly 32 from the surrounding environment as well as dust.

Lens 56 is capable of stationary mounting in arm 30 due to the elimination of the need to dynamically focus light from diode 44. The need to effect dynamic focussing has been eliminated as a result of the degree of stabilization provided to disc 20 and the predictability of the distance between disc 20 and lens 56 during operation. Such stabilization and predictability comes from two sources, namely from plate 66 provided in the preferred embodiment in cartridge 12 and from coupler 64. Plate 60 provides primary stabilisation while coupler 64 affords secondary stabilisation of the media. The surface of plate 66 which faces disc 20 is a Bernoulli surface which serves to create and maintain an air bearing between the disc qu.d plate 66. The structural features which result in r e creation of this air bearing by the Bernoulli surface are known and will not be repeated herein.

However the adoption of such phenomena to optical information storage systems in order to eliminate the Ieed for dynamically focussing light onto the disc is not known.

While plate 66 in the preferred embodiment is described as a part of cartridge 12, it is within the scope of the invention for plate 66 to be physically attached to drive 10. In such an alternative design, cartridge 12 would be construed to allow plate 66 to be positioned proximate disk 20 upon full insertion of cartridge 12.

Although disc 20 has been primarily stabilized by the air bearing created by plate 66, it will be recalled that optical head assembly 32 is accessing disc 20 through opening 18. Opening 18 is also present in plate 66. In the region within opening 18 there is no stabilization of disc 20. Consequently, coupler 64 serves to provide local secondary stabilization in the area surrounding lens 56 by creating and maintaining an air bearing which serves to hold that portion of disc 20 passing beneath coupler 64 in a close and, as will be desribed, predictable relationship thereto.Although the details of the structure contained in coupler 64 for achieving the creation of an air bearing have been described in US Patent No 4,414,592 - Losee et al, which is incorporated herein by reference, the adoption of such phenomena to optical information storage systems in order to eliminate the need for dynamically focussing light onto the disc is not known.

Referring to Figure 5, the surface of coupler 64 creates and maintains an air bearing between coupler 64 and disc 20. In the preferred embodiment the distance "A" between coupler and disc is approximately 5 to 10 microns plus or minus 0.5 microns. There are a number.of alternative coupler shapes and designs which are capable of providing the requisite media stabilisation. In one such design, this relationship between coupler 64 and disc 20 is achieved by providing a substantially flat surface 70 surrounding lens 56 (not shown) and a series of increasingly steeper surfaces adjoining surface 70.

It will be noted that in Figure 5 that such surfaces may not be easily distinguished and a certain degree of exaggeration of the arcuate shaped surfaces is necessary. In the preferred embodiment surface 72 is an arcuate surface formed as having an arc radius of approximately 500 mm, surface 74 is also an arcuate surface having an arc radius of approximately 270 mm and surface 76 is a generally flat conically shaped surface formed at an angle of approximately 45 with surface 70.

It will also be noted that the particular arc radii chosen for surfaces 72 and 74 will vary, depending on the properties of the media chosen such as stiffness, toughness, and presence and characteristics of lubrication. The arc radius of lens 56 (not shown in Figure 5) and the distance it protrudes from surface 70 are also dependent on the properties of the media chosen. In the preferred embodiment, the arc radius of lens 56 is approximately 50 mm and it protrudes approximately 0.02 mm from surface 70.

It is important to note that the structure of coupler 64 could be used to stabilize either rotatingflexible discs, such as disc 20, or tape forms of optical media. This structure is necessary only to achieve and maintain an air bearing between the optical head contained in coupler 64 and the media that is either being rotated, moved linearly past coupler 64 or helically scanned by a rotating drum, in geometries known in magnetic data recording technology.

Furthermore, it may not be necessary to provide plate 66 for Bernoulli stabilization of a rotating disc. Indeed, such stabilization is not necessary for tape media.

Therefore the present invention is applicable to both flexible optical discs and tape.

Referring to Figure 7, there is shown an alternate embodiment of the optical head assembly shown in Figure 6. Light passing through lens 50 is provided to prism 80 which is a combination anamorphic correction and polarizing beamsplitter prism. In order to reduce the size of the optical head assembly, it was found that a certain amount of anamorphic correction was necessary to the light emitted from diode 44 (not shown). The shape of prism 80 is chosen to make the first optical axis perpendicular to the last optical axis. Also, an objective lens 82 is substituted for the gradient index lens 56 shown in Figure 6. It has been found that the objective lens provides better wavefront aberration correction than the gradient index lens. A polarizing beamsplitter coating 84 is provided to reflect the light to lens 58.This light then has a plane of polarization which has been retarded by quarter-wave plate 54.

Referring to Figure 8, there is shown from a top view another alternative embodiment of the optical head assembly shown in Figure 6. In a similar fashion to the assembly shown in Figure 7, an objective lens 82 is provided for focussing light onto media 20 (not shown in Figure 8). A prism 84 is provided whereby lens 58 and lens 50 can now be positioned next to one another, further reducing the optical head assembly height. A polarizing beamsplitter coating 88 is again provided to reflect light into lens 58. A mirror surface 90 acts as a fold mirror to totally reflect light either from prism 86 to lens 82 or from lens 82 to prism 86.

Referring to Figure 9, there is shown another alternative embodiment of the optical head assembly shown in Figure 6. There may be conditions during which it will be desirable to provide a focussing action. To this end laser diode 44 is securely mounted to a solenoid-like device 92. Lens 50 and beamsplitter 52, however, are mounted on plunger 94 by strut members 96.

Device 92 is designed so that the distance between lens 50 and diode 44 can be selectively changed through the application of an appropriate signal on line 98 by processor 42. Such a signal would be provided in response to processor 42 determining from the signal provided by detector 60, the need for focussing the light. Methods for making such determinations are presently known in relation to dynamically focussed optical systems. Light emitted from beamsplitter 52 is then reflected by a prism having mirrored surface 98 through quarter-wave plate 54 and lens 56 onto the surface of disc 20.

Figures 10-13 relate to magneto-optical storage systems according to the invention. In the following description components relevant to the magneto-optical aspect of the invention are depicted by reference numerals greater than 100. As shown in Figure 10, cartridge 112 has been fully inserted and arm 130 has been extended such that the magneto-optic head assembly 132 has been moved radially across the surface of disc 120. It will be seen that arm 130 is split into upper arm half 130a and lower arm half 130b with disc 120 passing therebetween. Magneto-optical head assembly 132 is shown to be split between arm halves 130a and 130b for supporting the optical and magnetic portions of the head assembly. Consider first the optical portion of the head assembly supported by arm half 130a wherein there is shown laser diode 144 having leads 146. Although not shown, it will be understood that leads 146 are electrically connected to processor 42 (see Figure 2) for operation in any one of several known ways. Laser diode 144 serves as a source of light, the term "light" having the meaning previously discussed herein.

As shown in Figures 10 and 11, the light emitted from laser diode 144 is passed through and collimated by lens 150. Then this light is passed through polarizing beamsplitter 152, whereupon it is presented to prism 154 and reflected off or from mirror surface 155 towards or in the direction of disc 120. The lens 150 may be a gradient index lens. The light which is reflected by prism 154 is then passed through lens 156, which focusses the light onto the surface of disc 120. Unlike previous magneto-optical storage systems, lens 156 is not mounted in a fashion so as to be moved relative to arm 130. In this regard lens 156 is stationary in relation to arm 130. Light reflected off or from the surface of disc 120 is then again collimated by lens 156, passed through prism 154 and reflected by the mirror surface contained in beamsplitter 152.Since light is being reflected off or from the surface of disc 120, detection will be dependent upon the Kerr effect.

The light reflected from the media, termed the "read beam", has two possible orientations of its polarization plane, depending on the orientation of the magnetic moment at the reflection point on the media. Each of these orientations of the reflected light has its plane of polarisation rotated by a few degrees with respect to the plane of the illuminating beam's polarization. The read beam is recollimated by objective lens 156 and reflected by prism 153 back toward beam splitter 152. In the preferred embodiment, beamsplitter 152 is a leaky polarizing beamsplitter which will not only reflect the polarization component of the read beam which has been created by the rotation effect of the media, but which will also reflect a certain amount of the larger polarization component of the light which is in the original plane of the illuminating beam.Consequently, the part of the read beam reflected by beamsplitter 152 is an essentially constant fraction of the total intensity of the read beam incident on beamsplitter 152, but the rotational difference between the two possible polarization orientations is exaggerated. The read beam passes next through half-wave plate 157 to beam splitter 158, a polarization beamsplitter which splits the light into two component beams to be focussed by lenses 159a and 159b onto detectors 160a and 160b respectively. The lenses 156 and 159a and 159b may be gradient index lenses. Half-wave plate 157 serves as a rotator to rotate the polarization planes of the read beam approximately 45e adjusted so on average the intensities of the reflected and transmitted beams exiting beamsplitter 158 are equal.

While detectors 160a and 160b can be of several different types, one detector used-is the model IT338 manufactured and sold by Sony Corporation. Such a detector serves to detect or discern both data as well as tracking information. Detectors 160a and 160b, in turn, generate electrical signals reflective or indicative of the detected data and tracking information. These signals are then transmitted via leads 162 to processor 42. As previously explained, the signals from each of the detectors are compared in processor 42 in order to determine if any difference exists between the signals. The difference between the two signals is an indication of the magnetic domain polarity and hence the logic state stored at the reflection point on disc 120.For example, a positive difference is an indication of a digital 1 being stored at that point while a negative difference is an indication of a digital 0 being stored at that point.

The signals from the detectors not only serve to provide accessed information, but also allow processor 42 to evaluate the tracking information and provide or supply the appropriate signals to linear motor 134 for moving arm 130 in a manner so that magneto-optical head 132 can be radially positioned over, and follow, a desired track on disc 120. Lens 156 is securely mounted in support disc 164, which, in turn, is securely mounted in arm half 130a.

A magnetic head 170 is securely fastened in lower arm half 130b. By moving media between magnetic head 170 and lens 156, information can be magnetically recorded on disc 120 at those points heated by the light which is focussed by lens 156.

Lens 156 and magnetic head 170 are capable of stationary mounting in arm 130 due to the elimination of the need to dynamically focus the light emitted from diode 144. The need to dynamically focus this light has been eliminated as a result of the degree off stabilization provided to disc 120 and the predictability of the distance between disc 120 and lens 156 during operation. Such stabilization and predictability comes from two sources, namely from plate 166 provided in the preferred embodiment in cartridge 112 and from magnetic head 170. Plate 166 provides primary stabilisation while magnetic head 170 affords secondary stabilisation of the media. The surface of plate 166 which faces disc 120 is a Bernoulli surface which serves to create and maintain an air bearing between the disc and plate 166.The structural features which result in the creation of this air bearing by the Bernoulli surface are known and will not be repeated herein. However, the adoption of such phenomena to magneto-optical information storage systems in order to eliminate the need for dynamically focussing light onto the disc is not known.

Although plate 166 in the preferred embodiment is shown to be an integral part of cartridge 112, in an alternative configuration, plate 166 can be physically attached to drive 110. In this alternative design, cartridge 112 is appropriately modified, allowing plate 166 to be positioned proximate disc 120. Consequently, once cartridge 112 has been fully inserted into drive 110, the operation of the Bernoulli surface of plate 166 in providing the primary stabilization of disc 120 is essentially identical to that described above.

While not shown it will be understood that an opaque cover member may be provided over magneto-optical head assembly 132 in order to block out stray light as well as to protect magneto-optical head assembly 132 from the surrounding environment as well as dust.

Although disc 120 has been stabilized by the air bearing created by plate 166, it will be recalled that magneto-optical head assembly 132 is accessing disc 120 through opening 18. Opening 18 is also present in plate 166. In the region within opening 118 there is no stabilization of disc 120. Consequently magnetic head 170 serves to provide local secondary stabilization in the area surrounding lens 156 by creating and maintaining an air bearing which serves to hold that portion of disc 120 passing over magnetic head 170 in a close and, as will be described, predictable relationship thereto. Although the details of the structure contained in magnetic head 170 for achieving the creation of an air bearing have been described in US Patent No 4,414,592 - Losee et al the adoption of such phenomena to magneto-optical information storage systems in order to eliminate the need for dynamically focussing light onto the disc is not known.

Referring to Figure 12, the surface of coupler or magnetic head 170 creates and maintains an air bearing between magnetic head 170 and disc 120. In the preferred embodiment the distance "A" between the head and disc is app oximately 5-10 microns plus or minus 0.5 microns.

There are a number of alternative coupler shapes and designs which are capable of providing the requisite media stabilisation. In one such design, this relationship between magnetic head 170 and disc 120 is achieved by providing magnetic head 170 with a substantially flat surface 171 surrounding lens 156 (not shown) and a series of increasingly steeper surfaces adjoining surface 171. It will be noted that in Figure 12 that such surfaces may not be easily distinguished and a certain degree of exaggeration of the arcuate shaped surfaces is necessary.In the preferred embodiment, surface 172 is an arcuate surface formed as having an arc radius of 500 mm, surface 174 is also an arcuate surface having an arc radius of 500 mm, surface 174 is also an arcuate surface having an arc radius of 270 mm and surface 176 is a gen :1 lly flat surface formed at an angle of 45" with surface 171. Although not shown in Figure 12, a similar means of secondary stabilisation can be provided for the optical head assembly. In particular, stabilisation may be achieved around lens 156 by creating a similar set of arcuate shaped surfaces for coupler 164 surrounding lens 156.

Thus, it is within the scope of the invention to provide such stabilisation on either or both of magnetic head 170 and coupler 164.

It is important to note that the structure magnetic head 170 and coupler 164 could be used to stabilize either rotating flexible discs, such as disc 120, or tape forms of magneto-optic media. This structure is necessary only to achieve and maintain an air bearing between the magnetic head or the coupler and the media that is being rotated, moved linearly past the magnetic head or helically scanned by a rotating drum, in geometries known in magnetic data recording technology. Furthermore, it may not be necessary to provide plate 166 for Bernoulli stabilization of a rotating disc. Indeed, such stabilization is not necessary for tape media. Therefore the present invention is applicable to both magneto-optical discs and tape.

Since the surface of disc 120 is stabilized at a relatively fixed distance from magnetic head 170, it is possible for the first time to operate a magneto-optical storage system so that the magneto-optical head is continuously focussing light onto the surface of disc 120. Consequently, information is stored on disc 120 by changing the orientation of the magnetic field of the magnetic recording element of magnetic head 170. Since magnetic head 170 is of a size used to magnetically record information on so-called floppy discs, the problem of relatively slow switching of magnetic field orientation, present in previous devices, has been eliminated.

Referring to Figure 13, there is shown an alternative embodiment of the magneto-optical head assembly. Rather than split arm 130 into upper and lower halves, it may be desirable to position the magnetic recording head 170 and the optical head on the same side of disc 120. Since the object is to magnetically record in the same location, magnetic head 170 has been provided with a U-shaped magnetic element 180. Although not shown, it will be understood that magnetic element 180 is an electromagnet which is given a magnetic field in accordance with an electrical signal provided on leads 182. Light to be focussed onto the surface of disc 120 is directed between the arms 184a and 184b of element 80. The height of magnetic head 170 will have'to be taken into account.That is, since the magneto-optical head will be slightly further away from disc 120, this distance will have to be taken into account when choosing lens 156.

Consider now the magneto-optic information storage system during write and read operations. During a write operation, information to be written on the flexible media is organized by processor 42 for sequential storage onto disc 120. A signal is generated by processor 42 which activates laser diode 144, assuming that processor 42 has determined, from the signals received from detectors 160a and 160b, that the magneto-optical head assembly is positioned over a desired track on disc 120. With laser diode 44 activated, information to be written is stored on disc 20 by varying the orientation of the magnetic field of magnetic head 170 in a known manner. Since disc 120 is heated at the point where light from laser diode 1z.4 is focussed, the poles located within that heated area on the media will assume the orientation of the magnetic field produced by head 170.Such reorientation of poles on disc 120 will continue until processor 42 has written all of the information to be stored. It will. of course, be understood that while this write operation is taking place, disc 120 is spinning about hub 22 and linear motor 34 is moving arm 30 in a fashion to move magneto-optic head assembly 132 radially across disc 120 also in response to signals from processor 42.

During the read operation, light from laser diode 144 is focussed onto the surface of disc 120. It is not necessary and, in fact, it is preferred that the power associated with the read light be such that any heating of disc 120 by the light is minimal. Light reflected from the surface of disc 120 passes through the magneto-optical head in the manner already described and results in a series of electrical signals being generated and provided to processor 42. Processor 42 determines the difference between the signals from detectors 160a and 160b and uses this result to determine the presence of a logic 1 or a logic 0 stored on disc 20. Basically, if procesor 42 determines a difference in those signals from detectors 160a and 160b, there is a logic 1 present on the media. If there is no difference between the signals, then a logic 0 is present on the media.

While the invention has been described and illustrated with reference to specific embodiments, those skilled in the art will recognize that modification and variations may be made without departing from the principles of the invention as described herein above and set forth in the following claims. For example, in one alternative configuration, not shown, linear actuator motor 34 may be replaced by a rotary actuator motor. Such a device would move across the surface of disc 20 in a fashion which is similar to the motion of the tone-arm of a conventional phonograph.

Consequently, in such an embodiment, arm 30 and spicule member 28 would not have the shapes illustrated in Figure 1, but rather would be appropriately modified, allowing accurate positioning and movement of head assembly 32 across the surface of disc 20.

Claims (15)

1. An optical read/write storage system for reading and/or writing data to and from a flexible optical or magneto-optical media, comprising: an optical read/write head for providing focussed light onto said flexible media and for receiving reflected light from said flexible media; and fine stabilization means, associated with or connected to said optical head and positioned proximate said flexible media, for stabilizing said flexible media in 2 desired position so that said optical head need not be moved substantially toward or away from said media in order to maintain said light focussed on said media.

2. An optical read/write storage system for reading and/or writing data to and from a flexible optical or magneto-optical media, comprising: an optical read/write head for transmitting focussed light onto said flexible media and for detecting light gathered from said flexible media; and fine stabilization means, associated with or connected to said optical head and positioned proximate said flexible media, for stabilizing said flexible media in c desired position so that said optical head need not be moved substantially toward or away from said media in order to maintain said light focussed on said media.

3. The storage system of claim 1 or 2, further comprising gross stabilization means, positioned proximate said flexible media, for providing a gross stabilizing effect to said flexible media while reading and writing data, said gross stabilization means having an opening providing access to said flexible media.

4. An optical read/write storage system for reading and writing data to and from a flexible media, comprising: gross stabilization means, positioned proximate said flexible media, for providing a gross stabilizing effect to said flexible media while reading and writing data, said gross stabilization means having an opening providing access to said flexible media; a light source for providing light of a type suitable for reading and writing information onto said flexible media; a polarizing beamsplitter, positioned to receive said light from said source; movement means, connected to said beamsplitter, for positioning said beamsplitter over said flexible media so that said light from said source is reflected onto said flexible media; optical phase retarder means, positioned proximate said beamsplitter, for transforming polarization of said light as said light passes therethrough; lens means, positioned proximate said retarder means, for focussing said light passing through said retarder means onto said flexible media and for collecting reflected light from said flexible media and providing it to said retarder means; detector means, positioned proximate said beamsplitter, for receiving said reflected light and generating an information signal in response to such reception; and fine stabilization means, connected to said beamsplitter and positioned proximate said flexible media, for stabilizing said flexible media in a desired position so that said lens need not be moved substantially toward.or away from said media in order to maintain said light focussed on said media.

5. Apparatus for reading and/or writing a cartridgeenclosed flexible carrier with optically-detectable data, the cartridge having an opening therein through which the flexible carrier can be accessed, said apparatus comprising: means for receiving and locating a cartridge with the opening therein in a predetermined position; an optical system arranged to bring a light beam to a focus at a predetermined plane such that1 when the cartridge is inserted into the receiving means1 the light beam passes through the cartridge opening and said predetermined plane lies within the confines of the cartridge; means for rotating the flexible carrier about an axis substantially perpendicular to its plane; and Bernoulli-effect means for locally deflecting the flexible carrier in the region of said opening so as to bring the deflected portion of the carrier substantially into stable coincident relation with said predetermined plane whereby the light beam can be maintained focussed on the carrier without the need for focus adjustment while the carrier is rotating.

6. Apparatus as claimed in claim 5 in which the Bernoulli-effect means comprises a coupler having a surface arranged to register with said opening when the cartridge is inserted into the receiving means, the means, the coupler surface encircling the path of travel of the light beam through the coupler.

7. Apparatus as claimed in claim 5 in which the Bernoulli-effect means comprises a coupler having a surface arranged so as to be aligned with said opening when the cartridge is inserted into the receiving means, the coupler being disposed on the opposite side of the flexible carrier to the optical system.

8. Apparatus as claimed in claim 7 in which the coupler comprises magnetic means for use in effecting reading and/or writing of magneto-optical data.

9. Apparatus as claimed in claim 5 in which the Bernoulli-effect means comprises a first coupler having a surface arranged to register with said opening when the cartridge is inserted into the receiving means and a second coupler having a surface arranged so as to be aligned with said opening when the cartridge is inserted into the receiving means, the first and second couplers being located on opposite sides of said predetermined focussing plane of the light beam.

10. Apparatus as claimed in any one of claims 5-9 in which a Bernoulli plate is associated with the receiving means for effecting gross stabilisiation of the rotating carrier, said Bernoulli-effect means providing fine stabilisation of part of the carrier as the carrier surface traverses said opening.

11. Apparatus for reading and/or writing a flexible carrier tape with optically-detectable data, comprising: a read/write assembly including an optical system arranged to bring a light beam to a focus at a predetermined plane; means for transporting the tape along a path traversing the read/write assembly; and Bernoulli-effect means for locally deflecting the flexible tape in the vicinity of the read/write assembly so as to bring the deflected portion of the carrier substantially into stable coincident relation with said predetermined plane whereby the light beam can be maintained focussed on the tape without the need for focus adjustment while the tape is in motion past the read/write assembly.

12. Apparatus as claimed in claim 11 in which the Bernoulli-effect means comprises a coupler having a surface which is located in the region of the read/write assembly and over which the tape is passed as it traverses the read/write assembly.

13. Apparatus as claimed in any one of claims 6-10 and 11 which the (or each) coupler has a boundary where the coupler surface extends away from said predetermined plane.

14. Apparatus as claimed in claim 12 in which said boundary surface comprises a number of surface portions of differing inclination or radius of curvature.

15. An information read/write storage system for reading and/or writing data to and from a flexible magneto-optic media, comprising: a magnetic recording means, having a recording head positioned proximate said media, for recording information onto said media at a point, said point being defined as the area of said media wherein information is being recorded at any given time; and an optical read/write means for providing focussed light onto said media during reading and writing, for receiving reflected light from said media to read said information and for continuously providing focussed light onto said media for heating said point while said magnetic recording means is recording.